This invention relates to a method of impregnating leather with a material which is incorporated into the leather in a micro-encapsulated material.
In the leather processing industry, there is a large number of additives, agents, etc., which need to be impregnated into the body of the leather so that they can perform their required function effectively. In the past, such materials have been impregnated into the leather using a number of different processes according to the nature of the additive, agent, etc. The present invention is concerned with providing a general purpose method which is capable of impregnating a wide range of different materials into the leather, but using a generally similar process. Accordingly the present invention contemplates first encapsulating the material or agent into a micro-encapsulated form. Once in this form, the impregnation process may be determined substantially on the basis of the size and composition of the micro-capsule shells rather than exclusively on the basis of the material which is required to be added.
U.S. Pat. No. 4,510,188 describes a method for making a textile or leather material with a chromatic effect in which a layer of a micro-encapsulated liquid cholesteric crystal material is applied to the surface of the textile material or leather. The micro-encapsulated material is applied as a dispersion of capsules in a synthetic resin. In this process, the material is applied as a surfacial layer rather than being impregnated into the fibrous structure of the leather. The techniques of the present invention differ from the processes disclosed in U.S. Pat. No. 4,510,188 because they achieve actual impregnation of the encapsulated material at least partially into the leather rather than leaving the encapsulated material as a surfacial layer.
U.S. Pat. No. 5,368,609 discloses a process for softening leather in which thermoexpansible microcapsules (TEMCs) are impregnated into the leather and then caused to expand. The TEMCs contain a volatile liquid which is designed to evaporate and cause the capsule to expand by preferably ten to sixty times their original volume. This technique is concerned with the mechanical function of the microcapsules rather than using the capsules as a vehicle for impregnating material into the leather. The microcapsules are impregnated into the leather in a wet process.
German Published Application DE-A-3921145 discloses an arrangement for rendering leather surfaces matt. In this process a microcapsule material is applied to the surface of the leather by means of a spray gun, to provide a surfacial coating.
WO95/34609 discloses an arrangement in which a binder containing encapsulated phase change materials is coated to a leather substrate. This earlier document refers to a surfacial coating rather than a partial or complete impregnation of the leather material.
This invention is therefore concerned with providing a method whereby a wide range of different agents, additives, etc. may be incorporated into the leather to impart to it properties otherwise difficult or impossible to attain consistently and permanently in the context of normal use. Examples of such additives include biocides, scents, colourants, softening agents, fillers, levelling agents, fault observing agents, phase change materials, abrasion enhancers, magnetic substances, humectants, water-proofing agents and fire-retarding agents.
Furthermore the invention is concerned with selectively focusing the application of the micro-encapsulated material to the required region of the leather, whether this be impregnated throughout the thickness of the leather, confined to a restricted layer of the thickness at or below surface level, or additionally including a surfacial layer.
It will be appreciated that, in the leather processing industry, no two skins are identical and so it is therefore advantageous to be able to provide a general purpose process which provides generally consistent results within individual skins, from skin to skin within a process batch, and between process batches.
In the case of the phase change materials, it is particularly important to distribute the material in a substantially uniform manner through the depths of the leather to be treated. In addition the microencapsulation of the phase change material means that it retains its integrity within the micro-capsules and can cycle through the phase change without dispersing into the leather.
The phase change material provides the leather with a thermal buffer effect which can provide enhanced comfort for the user. If the leather is used e.g. in gloves, boots, shoes, etc, and intended for cold use, the melting point of the phase change material may be selected such that when the temperature of the leather falls below a certain threshold, the phase change material solidifies, giving up heat and warming the skin of the wearer. In the opposite sense, if the leather is meant for warm use, the phase change material may be selected to have a melting point such that increase of the leather temperature beyond a set level causes the material to melt and remove heat from the ambient, thereby cooling the skin of the wearer.
Accordingly, in one aspect, this invention provides a method of impregnating leather with a material, which comprises the steps of:
impregnating leather with a material, which comprises the steps of:
providing a micro-encapsulated supply of said material;
applying said micro-encapsulated material to the flesh side of said leather using a roller which applies pressure to said leather, thereby to cause said micro-encapsulated material to be impregnated in said leather.
Preferably said micro-encapsulated material is applied to the surface of said roller at a controlled rate, typically of between 60 g/m2 and 180 g/m2.
The micro-encapsulated material preferably has a capsule size in the range of from 5 to 40 microns.
The leather is preferably conveyed past said roller by a conveyor belt means. The conveyor belt means and said roller may have substantially the same linear speed and direction. However, in certain applications it may be desirable for the speeds to be different to provide a differential slip effect between the roller and the leather. In other instances it may be useful to have the roller and the conveyor belt means running in different directions to provide a strong scrubbing action.
Preferably the conveyor belt means and said roller have a linear speed of between 2 and 10 m/min.
The micro-encapsulated material is preferably in the form of a liquid slurry comprising an aqueous base and one or more agents selected from thickening agents, wetting agents, dispersants, and flow aids.
Preferably, the roller provides a compression action on the leather such that the roller gap is between 60% and 90% of the thickness of the uncompressed leather. This means that the leather is compressed as it passes under the roller and re-expands immediately thereafter and this action is thought to enhance absorption of the micro-encapsulated material into the fibrous matrix of the leather.
Although in many instances a single pass will be sufficient, the leather may be passed two or more times past the roller to achieve the required amount of impregnation.
One of the advantages of the method of this invention is that it allows a substantially uniform impregnation of the micro-encapsulated material throughout the fibrous matrix. This means that the packing density of the micro-encapsulated material within the leather for a given application rate is minimized, thereby reducing the effect that the impregnation has on the xe2x80x9cfeelxe2x80x9d of the leather. In the case of non-uniform impregnation near the surface of the leather, the packing density of the micro-encapsulated material is relatively high which means that the leather can feel stiff.
In another aspect, this invention provides a method of impregnating leather which comprises the steps of:
providing a micro-encapsulated supply of said material,
introducing said micro-encapsulated material into a drum containing said leather and a liquid float, and
drumming said micro-encapsulated material into said leather in a wet process.
Preferably said wet process is carried out at a temperature of between 40xc2x0 C. and 50xc2x0 C. The encapsulated material is preferably introduced into the wet process at rate of approximately 50% of the dry weight of the leather.
Although longer or shorter periods may be required, it is preferred for the drumming step to be performed for at least one hour.
The micro-encapsulated material may be drummed into the leather during a retanning process, in which the pH of the liquid float is preferably maintained at a value of from 5.5 to 6.0.
Alternatively or additionally, the micro-encapsulated material may be drummed into the leather during a dyeing process in which case the pH is preferably maintained at a value in the range of 6.0 to 7.5.
Additionally or alternatively, the material may be drummed into said leather during a fat-liquoring process, in which case the pH of the liquid float is preferably maintained at a value in the range of from 5.5 to 6.5.
The invention also extends to leather produced in accordance with this invention and to articles made wholly or partially of leather in accordance with this invention. Thus the leather may be used in gloves, footwear, clothing, leathergoods such as suitcases, wallets, straps, etc, and saddlery, and any other applications where dispersion of selected materials in said leather in micro-encapsulated form may prove beneficial.